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the later the menarche and the less the height and weight at all ages, both of the earlier and later born children. . . . (38, p. 27)
He mentions that this has been documented in Czechoslovakia and England and cites malnutrition or increased frequency of diseases, either of which might be associated with increased family size, as possible causal factors.
Douglas and his colleagues also looked into this in the National Survey of Health and Development mentioned earlier. In the first report of their observations (34), only the findings in girls were evaluated because they used menarche as their definitive sign of maturation and lacked an equally satisfactory criterion for boys. Noting the secular trend toward earlier menarche, which has been attributed at least in part to improved nutrition (38, 39, 40), Douglas found no social class differences, in spite of the considerable differences he had observed in growth.
A more detailed study of these families fails to show any positive association between poor living conditions and late puberty; in the middle classes it is the late developers who tend to come from the better homes, from those which were least crowded and best equipped. . . . (34, p. 108)
He did, however, find clear differences associated with family size, as shown in Table 8, in which an obvious relation between family size and menarche is apparent, and only girls may be seen to mature at substantially earlier ages. In a more recent follow-up of these same children, Douglas has
TABLE 8
Age of Puberty among a Sample of Girls in the National Survey of Health and Development by Completed Family Size, Great Britain, 1954-1957
Completed					
Family	Age at First Period				
(Number of	Earlya	Average"3	Latec	Total	of
Children)	(Percent)	(Percent)	(Percent)	(Percent)	Girls
1	53.0	28.3	18.7	100.0	219
2	39.2	36.1	24.7	100.0	502
3	36.0	33.6	30.4	100.0	342
4 or more	33.5	31.9	34.6	100.0	364
^Before 12 years 10 months.
12 years 10 months-13 years 9 months. cAfter 13 years 10 months.
Source: Douglas (34).y heights in boys, but the same trends are evident in her data for height and weight in both sexes. In order to examine this phenomenon further, she assigned a plus or minus "developmental level" (DL) based on the difference in centimeters between the measured height of a child and the expected average height for his age, using London data for comparison. The DL was assigned on the basis of heights obtained at or near age 8, to avoid growth variations produced by pubertal growth, and it allowed her to compare both boys and girls. She then compared the first and second child in consecutive pairs of children in families of different sizes and obtained the data shown in Table 7. As she noted, "the later-born child of any consecutive pair within a family tended to be taller than the preceding one." In her discussion, she noted: